A scintillator is a special material that exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, in other words they reemit the absorbed energy in the form of light.
A scintillation detector or scintillation counter is obtained when a scintillator is coupled to a light sensor such as a photomultiplier tube (PMT), photodiode, PIN diode or CCD-based photodetector. The light sensor will absorb the light emitted by the scintillator and reemit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those electrons (sometimes called photo-electrons) results in an electrical pulse that can be analyzed and provides meaningful information about the particle that originally struck the scintillator. In this way, the original amount of absorbed energy can be detected or counted.
The term “plastic scintillator” typically refers to a scintillating material where the primary fluorescent emitter, called a fluor, is suspended in a solid polymer matrix. While this combination is typically accomplished through the dissolution of the fluor prior to bulk polymerization, the fluor is sometimes associated with the polymer directly, either covalently or through coordination, as is the case with many Li6 plastic scintillators. Polyethylene naphthalate has been found to scintillate without any additives and is expected to replace existing plastic scintillators due to its higher performance and lower price.
The advantages of plastic scintillators include fairly high light output and a relatively quick signal, with a decay time between 2-4 nanoseconds. The biggest advantage of plastic scintillators, though, is their ability to be shaped, through the use of molds or other means, into almost any desired form with a high degree of durability.
In the field of medical radiation therapy, plastic scintillation detectors are used to convert radiation energy into light energy, and the light photons are counted to accurately determine the radiation dose. The scintillating plastic must transfer its photons to a device that can read them, which is commonly done by coupling one or more scintillating fibers to one or more plastic optical fibers (POF). The POF is then connected to a device that can read and analyze the optical output.
Manufacturing a high volume of such sensor cables is difficult because an accurate and repeatable connection of the plastic scintillator fiber to the plastic optical fiber is required. The problem arises from working with small diameter optical fibers that must be constructed accurately, yet at a low cost.
The current process used to create a sensor cable with a plastic scintillation detector relies on many precise, time-consuming steps. First, both ends of the scintillating fiber must be cut and polished. These cuts and polishes are difficult to do because the diameter (1 mm) and length (2 mm) of the scintillation fiber are very small. Next, the optical fiber must be cut, stripped and polished. Then the scintillating fiber is attached to the optical fiber with optical adhesive. A small piece of the optical fiber's jacket can be used to hold the two fibers in place when adhering. This step is challenging due to the small size of the fibers and the need to perfectly align their cores. A black paint or coating is then applied to the distal end of the fiber in order to keep the assembly light tight. The finished assembly is vulnerable to breakage because reliance is placed on the strength of the epoxy bond to hold the assembly together, and on a soft jacket material (PE or PVC) to hold the assembly in alignment. Due to the labor intensive process and time consuming steps, it is very expensive to produce a detector in this fashion, and the process also introduces variability from detector to detector. The current process also uses twist on (FC) or screw on (SMA) metal-bodied fiber connectors at the other end of the sensor cable. Applying these connectors adds more time to the process, and the FC and SMA connectors are expensive.
Therefore, a need exists for a novel manufacturing process and system for a radiation sensor cable to solve these problems.